1. Field of the Invention
The present invention relates to an inhaler which ejects medicine, aroma, nicotine or the like as liquid droplets and allows a user to inhale.
2. Related Background Art
In recent years, medical and science advances have increased average lifetime, thus having created an aging society. Conversely, discovery of new diseases or infections due to changes in dietary life or life environment, environmental pollution, virus, bacteria or the like has increased people's health anxiety. Especially, countries called advanced countries have problems of increases in patients who have adult diseases such as diabetes mellitus or hypertension and need for improvement of medical cure.
For example, a patient who has diabetes mellitus, above all, insulin-dependent diabetes mellitus called I type must have insulin regularly administered because insulin is not secreted from the pancreas. The administration of insulin has been presently performed with hypodermic injection, which places physical and mental burdens on a user. To relieve the burdens onto the user, pen type injection syringes having a fine needle which will not give high pains have been also developed. However, many patients who have I-type diabetes mellitus have the same life as healthy people, except when insulin is required to be regularly administered. Accordingly, mental resistance against injection administration in public even with a pen type will make it difficult to perform administration at an appropriate time. Thus, such a method has a possibility of no implementation of appropriate procedures to users.
On the other hand, a method of taking medicine by user's inhalation through an inhaler has been developed as another resolution. Such medicine administration through a respiratory system will cause no pain during injection. As an example of the inhaler, there have been known inhalers using a principle of ink jet type for an ejection device (see International Publication Nos. WO1995/001137 and WO2002/004043).
Such inhalers require accurate control of the amount and interval of medicine administration according to prescription, appropriate ejection control and highly efficient medicine administration. For example, the diameter of liquid droplet of medicine at a suction port of the inhaler (a portion which is put in a user's mouth to inhale medicine) has an effect on a probability of reaching the lung alveoli. Accordingly, it is preferable to use an inhaler capable of attaining liquid droplets having a constant droplet diameter regardless of use environments. Ejected droplets of medicine are carried to suction port side on air flows generated by inhalation. Accordingly, it is common that water moisture is evaporated from the liquid droplets until the droplets reach the suction portion and the diameter of liquid droplet decreases. However, the inhaler is used under various environments different in humidity or temperature, and the amount of water vaporization from the ejected liquid droplets changes with a use environment. In other words, even if respective liquid droplets having a same diameter are always ejected, the diameter of the liquid droplet at the suction port may change with a use environment, which may be a cause for difficulty in performing inhalation of an appropriate dose prescribed by a doctor. As a resolution to solve such problems, there has been conventionally proposed an inhaler having a function of promoting evaporation using a heater and a dehumidifier and keeping the diameter of a liquid droplet constant (see International Publication No. Number WO1996/009846). As another resolution for promoting evaporation, there has been proposed an inhaler which extends an air flow path of a mouthpiece (see International Publication No. WO2000/024362).
Because a patient who has I-type diabetes mellitus requires regular administration, such an inhaler is always carried. Accordingly, the inhaler should be capable of inhaling liquid droplets having a constant diameter regardless of use environments and be of a small and lightweight type.
However, the inhaler disclosed in International Publication No. WO1996/009846 requires a heater and a dehumidifier as a gas generator for promoting vaporization. Provision of all energy for driving the inhaler in the inhaler in view of portability requires inclusion of energy consumed in the generator, which is a cause for increasing the size and weight of the inhaler.
The inhaler disclosed in International Publication No. WO2000/24362 has not clearly described based on what variable, an air flow path length of a mouthpiece should be controlled, in extending the mouthpiece flow path, in order to control a change in a droplet diameter with evaporation.